1. Field of the Invention
The present invention relates to a wide-angle converter lens which can be mounted on an imaging lens used for a digital still camera, a video camera, a broadcasting camera, or the like, particularly, an imaging lens of which a variable magnification ratio is 10 or more, and of which a half angle of view ω at a wide-angle end is 30° or more.
2. Description of the Related Art
There have been conventionally proposed many wide-angle converter lenses, each of which is mounted on an object side of an imaging lens (master lens) and which changes a focal length of an entire photographing system to be short in the state of maintaining a focal plane of the entire system at a constant position.
For example, U.S. Pat. No. 7,463,424 discusses a wide-angle converter lens which includes, in order from an object side, a first lens unit having negative refractive power and a second lens unit having positive refractive power, in which four lens elements constitute an afocal system as a total system, and of which the focal length conversion magnification ratio is about 0.8.
Japanese Patent Application Laid-Open No. 2006-119346 discusses a wide-angle converter lens which includes a first lens unit configured with two lenses having negative refractive power and a second lens unit configured with a lens having negative refractive power and a lens having positive refractive power, and of which the focal length conversion magnification ratio is about 0.65.
However, in U.S. Pat. No. 7,463,424, if the wide-angle converter lens is mounted on an imaging lens (hereinafter also referred to as “master lens”), axial chromatic aberration (longitudinal chromatic aberration) at the telephoto end with respect to a reference wavelength is in the “under” state for g-line, so that the achromatic balance of the imaging lens is changed.
In addition, in Japanese Patent Application Laid-Open No. 2006-119346, if the wide-angle converter lens is mounted on an imaging lens (master lens), similarly to U.S. Pat. No. 7,463,424, axial chromatic aberration at the telephoto end with respect to a reference wavelength is in the “under” state for g-line and in the “over” state for C-line. In other words, the achromatic balance of the imaging lens is changed.
In other words, if such a wide-angle converter lens described above is mounted on the imaging lens, the balance of chromatic aberration from the middle zoom range to the telephoto end, particularly, the balance of axial chromatic aberration is deteriorated.